/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to you under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.logging.log4j.core.util;

import java.lang.reflect.Array;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * A bounded buffer containing elements of type T. When the number of elements to be added will exceed the
 * size of the buffer the oldest element will be overwritten. Access to the buffer is thread safe.
 * @param <T> The type of object stored in the buffer.
 */
public final class CyclicBuffer<T> {
    private final T[] ring;
    private int first = 0;
    private int last = 0;
    private int numElems = 0;
    private final Class<T> clazz;
    private final Lock lock = new ReentrantLock();

    /**
     * Instantiates a new CyclicBuffer of at most <code>maxSize</code> events.
     * @param clazz The Class associate with the type of object in the buffer.
     * @param size The number of items in the buffer.
     * @throws IllegalArgumentException if the size is negative.
     */
    public CyclicBuffer(final Class<T> clazz, final int size) throws IllegalArgumentException {
        if (size < 0) {
            throw new IllegalArgumentException("The maxSize argument (" + size + ") cannot be negative.");
        }
        this.ring = makeArray(clazz, size);
        this.clazz = clazz;
    }

    @SuppressWarnings("unchecked")
    private T[] makeArray(final Class<T> cls, final int size) {
        return (T[]) Array.newInstance(cls, size);
    }

    /**
     * Adds an item as the last event in the buffer.
     * @param item The item to add to the buffer.
     */
    public void add(final T item) {
        lock.lock();
        try {
            if (ring.length > 0) {
                ring[last] = item;
                if (++last == ring.length) {
                    last = 0;
                }

                if (numElems < ring.length) {
                    numElems++;
                } else if (++first == ring.length) {
                    first = 0;
                }
            }
        } finally {
            lock.unlock();
        }
    }

    /**
     * Removes all the elements from the buffer and returns them.
     * @return An array of the elements in the buffer.
     */
    public T[] removeAll() {
        lock.lock();
        try {
            final T[] array = makeArray(clazz, numElems);
            int index = 0;
            while (numElems > 0) {
                numElems--;
                array[index++] = ring[first];
                ring[first] = null;
                if (++first == ring.length) {
                    first = 0;
                }
            }
            return array;
        } finally {
            lock.unlock();
        }
    }

    /**
     * Determines if the buffer contains elements.
     * @return true if the buffer is empty, false otherwise.
     */
    public boolean isEmpty() {
        lock.lock();
        try {
            return 0 == numElems;
        } finally {
            lock.unlock();
        }
    }
}
